C-reactive protein as a possible diagnostic and prognostic factor of diabetic retinopathy

Background. Current data show an important role of C-reactive protein (CRP) in the onset and progression of diabetic retinopathy (DR), which necessitated the study of using its serum content as a possible contributing factor. Aim of the study was to determine the content of CRP at different stages of DR and the possibility of using it as a prognostic factor of its progression. Materials and methods. 136 patients with type 2 diabetes mellitus were examined and divided into groups: first — with non-proliferative DR (NPDR; 60 eyes), second — with preproliferative DR (PPDR; 42 eyes) and third — with proliferative DR (PDR; 34 eyes). Patients were examined and treated for 2 years. Serum content (in μg/l) of high-sensitivity (hs) CRP was determined by the enzyme-linked immunosorbent assay. The analysis of the study results was performed in the EZR v.1.54 package (Austria). Results. Patients with type 2 diabetes and DR reported a significant increase in serum hs-CRP compared to individuals without diabetes. In NPDR, it exceeded the control level by 1.9 times, in PPDR — by 3.2 times, in PDR — by 4.9 times (p < 0.001 for all comparisons). The selection of optimal thresholds for multi-class classification by the One-vs-All method with the construction of receiver operating characteristic (ROC) curves determined the cut-off levels of hs-CRP at different stages of DR. Values less than 1977 μg/l were characteristic of the control group. In patients with NPDR, the indicators ranged from 1978 to 3683.5 μg/l, in PPDR — from 3683.6 to 5523 μg/l, and in PDR, they were more than 5523 μg/l. The content of hs-CRP directly correlated with fasting glycemia (r = 0.194), central retinal thickness (r = 0.517) and volume (r = 0.486), glycated hemoglobin (r = 0.774), total cholesterol (r = 0.385), high-density lipoprotein (r = 0.260), low-density lipoprotein (r = 0.361), and very low-density lipoprotein (r = 0.493), as well as triglycerides (r = 0.374). The risk of DR progression after 2 years of observation increased 2.3 times for every 1000 μg/l increase in the hs-CRP blood content (p < 0.001; odds ratio = 2.33; 95% confidence interval (CI) 1.74–3.14). The area under the ROC curve was 0.84 (95% CI 0.77–0.90), the sensitivity of the model was 69.6 % (95% CI 60.7–81.8), specificity — 91.2 % (95% CI 83.7–97.4). Conclusions. The results obtained justify the possibi­lity of using C-reactive protein as a highly informative biomarker for diagnosing the stage of DR and predicting its progression.